142 FLIGHT International, 25 January 1962
Missiles and Spaceflight
SEASLUG DEVELOPMENT
A common key applies to these four
cutaway drawings portraying the
evolution of Seaslug Mk I through a
series of test vehicles. A, telemetry;
6, rear boost sockets: C, wing strong
ring; D, nitrogen control system;
E, ballast; F, instrumentation; G,
nitrogen bottles; H, flares; J, GFC
Seaslug Story
ON January 18 a paper entitled The Development of Seaslug was
read before the Astronautics and Guided Flight section of the Royal
Aeronautical Society by C. Bayly, MnuechE, FRAes, and A. Lightbody,
DCAe, BSC, MiMechE, FRAes, respectively general manager and techni
cal executive (armaments) of Whitworth Gloster Aircraft Ltd.
This was the first time that the principal industrial contractor for the
Royal Navy's medium ship-to-air guided weapon has described
its evolution publicly; this journal printed a preliminary account on
November 21, 1958.
Seaslug (said the lecturers) descended from LOP/GAP (liquid-
oxygen/petrol, guided air projectile) initiated for the Royal Navy in
1944. After feasibility studies at Westcott in 1946-47 the project was
transferred to industry in 1948, thereby becoming the first Service
guided weapon to have been worked on in either Government
establishments or industry. Sir W. G. Armstrong Whitworth
Aircraft (now Whitworth Gloster Aircraft) were appointed design
co-ordinators of a team consisting of GEC and Sperry Gyroscope,
respectively responsible for the guidance and the control system.
By January 1951 the basis of the design had been agreed, with a
body 16in diameter and 19ft 6in long, and the first test vehicle had
been successfully flown. The following key decisions were taken:
to use a nitric acid and kerosine sustainer motor, and four solid-
propellant boost motors wrapped round the forebody to obviate
the need for boost stabilizer fins; and to employ beam-riding
guidance (using the Type 901 radar designed for LOP/GAP), with
fixed wings and in-line rear controls in cartesian configuration.
Preceding the operational weapon came a series of test vehicles.
The first of these was the STV, boosted by four pairs of Demon
motors, with which the boost separation techique was proved
during tests at Aberporth and Woomera. It was followed by the
MTV/C [first drawing above], without a sustainer but including
the complete control system, guidance receiver and extensive
telemetry. Then came the MTV/H, incorporating an acid/methanol
sustainer and requiring four triple Demon boosts. This had one of
the first nitric-acid systems with a shelf life of two years.
In 1952 it was decided to procure from ICI a solid sustainer
motor, and development of the prototype solid, or P(S), missile
parallelled that of the liquid P(L). In the latter the tanks and
plumbing were drastically simplified, and a shelf life greater than
three years was obtained, but in 1955 the decision was taken to dis
card the liquid sustainer and concentrate on the P(S). Subsequently
the improved P(G) series was very successfully fired from HMS
Girdle Ness, leading up to the SC, or Seaslug Mk 1, which has now
completed its acceptance trials and is in production.
Construction The last of the cutaway drawings illustrates the
Mk 1 Seaslug, showing the division into interchangeable sections.
The fuze compartment is replacable as a unit on the boosted weapon,
and it is followed by the safety and arming unit and warhead, which
for trials purposes may be replaced by the telemetry illustrated.
Each of the four wings and four control fins are interchangeable,
and the three large packages housing guidance, controls and power
supplies occupy the section between them. All major handling and
launching loads act through the rear boost attachments on to the
wing strong ring, thus minimizing the weight penalty for non-flight
loadings (particularly important in view of the Admiralty need to
withstand the shock of nearby explosions). The wing is a light-alloy
structure which concentrates loads to a single high-tensile steel
spigot, while the control fins are machined fight-alloy forgings. The
main part of the body is the shell of the sustainer motor.
Guidance After the missile has been gathered in a wide-angle
beam, a rearward-looking aerial in the boat-tail of the missile
receives the pencil beam of the 901 radar, which presents the control
system with two voltages corresponding to up/down and left/right
demands to keep the missile in the centre of the beam. When firing
at low angles of elevation the scan pattern of the gathering beam
is offset upwards to prevent missiles from being lost in the sea.
a form of modulation being used to bring the missile down to the
guiding beam. Airborne equipment comprises the aerial in the rear
face of the boat-tail and the guidance receiver. The latter has
evolved through a number of prototype stages to a printed-circuit
and potted package measuring 27in X 11 in x 5 Jin and containing
approximately 100 valves and 500 resistors and capacitors.